let welcome = 'hello'
welcome() // 此⾏报错：TypeError: welcome is not a function

const str = Date.now() % 2 ? '奇数' : '偶数'

if (str !== '奇数') {
alert('hello')
} else if (str === '偶数') {
alert('world')
}

const obj = {width: 10, height: 15}
const area = obj.width * obj.heigh;

const message = `hello, world`
message.toUperCase()